set aStr to "これは秘密のInformationです。" –Alphabet & Numeric以外でも置換可能
set bStr to makeUnprintableChars(aStr)
–>　　"xxxxxxXxxxxxxxxxxxx。"

on makeUnprintableChars(aStr)
　　set anNSString to current application’s NSString’s stringWithString:aStr
　　set anNSString to anNSString’s stringByReplacingOccurrencesOfString:"[＼＼p{Lu}＼＼p{Lt}＼＼p{Nd}]" withString:"X" options:(current application’s NSRegularExpressionSearch) range:{0, anNSString’s |length|()}
　　set anNSString to anNSString’s stringByReplacingOccurrencesOfString:"[＼＼p{Ll}＼＼p{Lm}＼＼p{Lo}]" withString:"x" options:(current application’s NSRegularExpressionSearch) range:{0, anNSString’s |length|()}
　　return anNSString as text
end makeUnprintableChars